This invention relates to the preparation of novel additives for use in hydraulic cement compositions and particularly oil well cementing compositions and processes, and to methods for producing these novel additives.
The subterranean geological formations penetrated by well bores for production of petroleum and gas have been at increasingly greater depths, encountering in the process, an increasingly rigorous environment including significantly higher temperatures. In addition, an increasing number of wells requiring cementing are also disposed in offshore salt water environments so that the cementing compositions must manifest a compatibility with, or tolerance to, salt.
The cementing compositions are used particularly for sealing or cementing the annular space in a well bore between the casing of the well and the formation surrounding the casing. In practice the cementing composition is incorporated in a slurry, using, desirably, and by way of illustration, where an offshore well is being cemented, sea water to form the slurry. The slurry is pumped down through the well casing, into the formation and up the outside of the casing to effect the requisite seal.
As more rigorous conditions are encountered the need increases for improved additives to prevent the premature setting of the cement slurry with substantial or complete elimination of unpredictability of the cement composition and its retarding additives, including particularly, pseudosetting or gelation, in which state the cement attains a viscosity rendering it difficult or impossible to pump.
Accordingly, the invention is described in context with well cementing where the compounds of the invention have particular utility as cement retarding agents capable of significantly reducing or eliminating these difficulties, although other applications of the invention will be readily evident to those skilled in the art to which this invention pertains.
Considerations relevant to well cementing and the practices utilized in this field heretofore are described in the Report Prepared By The API MID-CONTINENT DISTRICT STUDY COMMITTEE OR CEMENTING PRACTICES AND TESTING OF OIL-WELL CEMENTS issued by AMERICAN PETROLEUM INSTITUTE ("API"), Division of Production, in Dallas, Texas 75201 as API Bulletin D-4, Corrected Edition of March 1963, entitled "The Effects Of Drilling-Mud Additives On Oil-Well Cements"; "API Specification For Oil-Well Cements And Cement Additives" (API Std 10A, Fourteenth Edition, dated April, 1969) and the "API Recommended Practice For Testing Oil-Well Cements And Cement Additives" (API RP 10B, Sixteenth Edition, dated April, 1969).
Numerous lignin compositions have been proposed heretofore for use as retardants in well cementing compositions and operations and are described, for example, in U.S. Pat. Nos. 2,880,102; 2,491,832; and 4,065,313. These include alkaline oxidized, hydrolyzed and partially desulfonated lignosulfonates that have been subsequently resulfonated which have been found to constitute effective, heat stable, and predictable retardants which reduce or eliminate the undesired gelation of many of the cement compositions in many of the more extreme environments in which they are incorporated.
Other patents of interest in this area include: U.S. Pat. Nos. 3,468,377; 3,478,823; 3,384,171; 3,700,031; 3,476,188; 3,532,166; U.S. Pat. Nos. 3,520,366; 3,553,130 and 3,688,844.
However, as ever more rigorous environments are explored for petroleum and natural gas, further improvements in communicating predictability, thermal stability, and resistance to pseudosetting of well cement slurries becomes necessary; and if material improvements in these characteristics could be achieved with maintenance of the other characteristics including salt tolerance and compatibility with a wide range of other components and cements, a significant advance in the state of the art will have been achieved.